Image scanners are widely used for scanning images of documents, photographs or films. The scanned images can be converted into electronic files, which are then stored, processed or spread. With increasing development of scanning technologies, the image scanners have experienced great growth and are now rapidly gaining in popularity.
In the early stage, the image scanner can scan one side of the document. For scanning both sides of the document, after one side of the document has been scanned, the document should be manually turned over so as to scan the other side of the document. As known, the process of manually turning over the document is troublesome. For solving the drawbacks, an automatic document feeder is usually integrated into the scanning apparatus. After a stack of documents to be scanned are placed on the sheet input tray of the automatic document feeder, the sheet-feeding mechanism of the automatic document feeder will successively transport the sheet to perform the scanning operation without the need of manually turning over the documents.
As the demand on the duplex scanning operation is gradually increased, a duplex scanning apparatus is disclosed for automatically performing the duplex scanning operation in order to scan both sides of the document.
Generally, the duplex scanning apparatuses are classified into two types. The first type of duplex scanning apparatus uses only one scanning module to scan both sides of the document. Since there is only one scanning module, a specified mechanism is required to turn over the document after one side of the document has been scanned. For performing the duplex scanning operation by the duplex scanning apparatus, the document needs to pass through the scan region for two or three times. As a consequence, the duplex scanning operation by the duplex scanning apparatus having one scanning module is also referred as a two-pass or three-pass scanning operation. The use of this duplex scanning apparatus to perform the duplex scanning operation, however, is time-consuming.
The second type of duplex scanning apparatus has two scanning modules. These two scanning modules are disposed at bilateral sides of the scan region. When the document is transported across the scan region, the two scanning modules simultaneously scan front and back sides of the document. In other words, the document needs to pass through the scan region for only one time to perform the duplex scanning operation. As a consequence, the duplex scanning operation by the duplex scanning apparatus having two scanning modules is also referred as a one-pass scanning operation. In comparison with the first type, the second type of duplex scanning apparatus has an increased scanning speed.
With increasing development of scanning apparatuses, the above two types of duplex scanning apparatuses fail to meet the users' requirements. For solving these drawbacks, Taiwanese Patent Publication No. 00571561 discloses a duplex scanning apparatus for performing a one-pass scanning operation without the need of manually turning over the documents. This duplex scanning apparatus comprises a scanning module. FIG. 1 is a schematic view illustrating a conventional duplex scanning apparatus disclosed in Taiwanese Patent Publication No. 00571561. As shown in FIG. 1, the conventional duplex scanning apparatus 1 comprises an automatic document feeder 11 and a scanning module 12. The scanning module 12 comprises a light source 121, a reflective mirror 122, a lens 123 and an optical sensing element 124. The automatic document feeder 11 comprises a sheet input tray 111, a sheet inverting region 112, a sheet ejecting tray 113, a first scan region 114, a second scan region 115, a light-transmissive channel 116, and a plurality of sheet transfer rollers 1171, 1172, 118 and 119.
For performing a duplex scanning operation on a document (not shown) by the duplex scanning apparatus 1, the document is fed into the internal portion of the duplex scanning apparatus 1 through the sheet input tray 111 and transported by the transfer rollers 1171 and 1172. When the document is transported across the first scan region 114, the light beam emitted by the light source 121 of the scanning module 12 is transmitted through the light-transmissive channel 116 and projected on a first side of the document. The light beam is reflected by the document and then directed to the reflective mirror 122. The light beam is then reflected by the reflective mirror 122 and transmitted through the lens 123. Next, the light beam is received by the optical sensing element 124, thereby obtaining the image of the first side of the document. Next, the document is transported across the sheet inverting region 112, and then transported to the second scan region 115 by the sheet transfer roller 118. After the document is transported across the sheet inverting region 112, the document is turned over. When the document is transported across the second scan region 115, a second side of the document is scanned by the scanning module 12 according to the above-mentioned method. Afterwards, the document is transported by the sheet transfer roller 119 and then exited from the duplex scanning apparatus 1 through the sheet ejecting tray 113.
From the above discussion, it is found that the scanning module 12 of the conventional duplex scanning apparatus 1 could scan the first side and the second side of the document at the first scanning region 114 and the second scan region 115, respectively. The conventional duplex scanning apparatus 1, however, still has some drawbacks. Since the distance between the light source 121 and the first scanning region 114 is too far, the brightness of the light beam emitted by the light source 121 is too weak, and the light beam emitted by the light source 121 usually fails to be effectively projected on the document. Under this circumstance, the efficacy of performing duplex scanning operation is insufficient. Even if the intensity of the light source is increased to be projected on the document, the scanning quality is still deteriorated.